/***
 * ASM: a very small and fast Java bytecode manipulation framework
 * Copyright (c) 2000-2007 INRIA, France Telecom
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the copyright holders nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */
package org.objectweb.asm.commons;

import java.io.ByteArrayOutputStream;
import java.io.DataOutput;
import java.io.DataOutputStream;
import java.io.IOException;
import java.security.MessageDigest;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;

import org.objectweb.asm.ClassAdapter;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.FieldVisitor;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

/**
 * A {@link ClassAdapter} that adds a serial version unique identifier to a
 * class if missing. Here is typical usage of this class:
 * 
 * <pre>
 *   ClassWriter cw = new ClassWriter(...);
 *   ClassVisitor sv = new SerialVersionUIDAdder(cw);
 *   ClassVisitor ca = new MyClassAdapter(sv);
 *   new ClassReader(orginalClass).accept(ca, false);
 * </pre>
 * 
 * The SVUID algorithm can be found <a href=
 * "http://java.sun.com/j2se/1.4.2/docs/guide/serialization/spec/class.html"
 * >http://java.sun.com/j2se/1.4.2/docs/guide/serialization/spec/class.html</a>:
 * 
 * <pre>
 * The serialVersionUID is computed using the signature of a stream of bytes
 * that reflect the class definition. The National Institute of Standards and
 * Technology (NIST) Secure Hash Algorithm (SHA-1) is used to compute a
 * signature for the stream. The first two 32-bit quantities are used to form a
 * 64-bit hash. A java.lang.DataOutputStream is used to convert primitive data
 * types to a sequence of bytes. The values input to the stream are defined by
 * the Java Virtual Machine (VM) specification for classes.
 * 
 * The sequence of items in the stream is as follows:
 * 
 * 1. The class name written using UTF encoding.
 * 2. The class modifiers written as a 32-bit integer.
 * 3. The name of each interface sorted by name written using UTF encoding.
 * 4. For each field of the class sorted by field name (except private static
 * and private transient fields):
 * 1. The name of the field in UTF encoding.
 * 2. The modifiers of the field written as a 32-bit integer.
 * 3. The descriptor of the field in UTF encoding
 * 5. If a class initializer exists, write out the following:
 * 1. The name of the method, &lt;clinit&gt;, in UTF encoding.
 * 2. The modifier of the method, java.lang.reflect.Modifier.STATIC,
 * written as a 32-bit integer.
 * 3. The descriptor of the method, ()V, in UTF encoding.
 * 6. For each non-private constructor sorted by method name and signature:
 * 1. The name of the method, &lt;init&gt;, in UTF encoding.
 * 2. The modifiers of the method written as a 32-bit integer.
 * 3. The descriptor of the method in UTF encoding.
 * 7. For each non-private method sorted by method name and signature:
 * 1. The name of the method in UTF encoding.
 * 2. The modifiers of the method written as a 32-bit integer.
 * 3. The descriptor of the method in UTF encoding.
 * 8. The SHA-1 algorithm is executed on the stream of bytes produced by
 * DataOutputStream and produces five 32-bit values sha[0..4].
 * 
 * 9. The hash value is assembled from the first and second 32-bit values of 
 * the SHA-1 message digest. If the result of the message digest, the five
 * 32-bit words H0 H1 H2 H3 H4, is in an array of five int values named 
 * sha, the hash value would be computed as follows:
 * 
 * long hash = ((sha[0] &gt;&gt;&gt; 24) &amp; 0xFF) |
 * ((sha[0] &gt;&gt;&gt; 16) &amp; 0xFF) &lt;&lt; 8 |
 * ((sha[0] &gt;&gt;&gt; 8) &amp; 0xFF) &lt;&lt; 16 |
 * ((sha[0] &gt;&gt;&gt; 0) &amp; 0xFF) &lt;&lt; 24 |
 * ((sha[1] &gt;&gt;&gt; 24) &amp; 0xFF) &lt;&lt; 32 |
 * ((sha[1] &gt;&gt;&gt; 16) &amp; 0xFF) &lt;&lt; 40 |
 * ((sha[1] &gt;&gt;&gt; 8) &amp; 0xFF) &lt;&lt; 48 |
 * ((sha[1] &gt;&gt;&gt; 0) &amp; 0xFF) &lt;&lt; 56;
 * </pre>
 * 
 * @author Rajendra Inamdar, Vishal Vishnoi
 */
public class SerialVersionUIDAdder extends ClassAdapter {

	/**
	 * Flag that indicates if we need to compute SVUID.
	 */
	protected boolean computeSVUID;

	/**
	 * Set to true if the class already has SVUID.
	 */
	protected boolean hasSVUID;

	/**
	 * Classes access flags.
	 */
	protected int access;

	/**
	 * Internal name of the class
	 */
	protected String name;

	/**
	 * Interfaces implemented by the class.
	 */
	protected String[] interfaces;

	/**
	 * Collection of fields. (except private static and private transient
	 * fields)
	 */
	protected Collection svuidFields;

	/**
	 * Set to true if the class has static initializer.
	 */
	protected boolean hasStaticInitializer;

	/**
	 * Collection of non-private constructors.
	 */
	protected Collection svuidConstructors;

	/**
	 * Collection of non-private methods.
	 */
	protected Collection svuidMethods;

	/**
	 * Creates a new {@link SerialVersionUIDAdder}.
	 * 
	 * @param cv
	 *            a {@link ClassVisitor} to which this visitor will delegate
	 *            calls.
	 */
	public SerialVersionUIDAdder(final ClassVisitor cv) {
		super(cv);
		svuidFields = new ArrayList();
		svuidConstructors = new ArrayList();
		svuidMethods = new ArrayList();
	}

	// ------------------------------------------------------------------------
	// Overriden methods
	// ------------------------------------------------------------------------

	/*
	 * Visit class header and get class name, access , and intefraces
	 * informatoin (step 1,2, and 3) for SVUID computation.
	 */
	public void visit(final int version, final int access, final String name, final String signature, final String superName,
			final String[] interfaces) {
		computeSVUID = (access & Opcodes.ACC_INTERFACE) == 0;

		if (computeSVUID) {
			this.name = name;
			this.access = access;
			this.interfaces = interfaces;
		}

		super.visit(version, access, name, signature, superName, interfaces);
	}

	/*
	 * Visit the methods and get constructor and method information (step 5 and
	 * 7). Also determince if there is a class initializer (step 6).
	 */
	public MethodVisitor visitMethod(final int access, final String name, final String desc, final String signature, final String[] exceptions) {
		if (computeSVUID) {
			if ("<clinit>".equals(name)) {
				hasStaticInitializer = true;
			}
			/*
			 * Remembers non private constructors and methods for SVUID
			 * computation For constructor and method modifiers, only the
			 * ACC_PUBLIC, ACC_PRIVATE, ACC_PROTECTED, ACC_STATIC, ACC_FINAL,
			 * ACC_SYNCHRONIZED, ACC_NATIVE, ACC_ABSTRACT and ACC_STRICT flags
			 * are used.
			 */
			int mods = access
					& (Opcodes.ACC_PUBLIC | Opcodes.ACC_PRIVATE | Opcodes.ACC_PROTECTED | Opcodes.ACC_STATIC | Opcodes.ACC_FINAL
							| Opcodes.ACC_SYNCHRONIZED | Opcodes.ACC_NATIVE | Opcodes.ACC_ABSTRACT | Opcodes.ACC_STRICT);

			// all non private methods
			if ((access & Opcodes.ACC_PRIVATE) == 0) {
				if ("<init>".equals(name)) {
					svuidConstructors.add(new Item(name, mods, desc));
				} else if (!"<clinit>".equals(name)) {
					svuidMethods.add(new Item(name, mods, desc));
				}
			}
		}

		return cv.visitMethod(access, name, desc, signature, exceptions);
	}

	/*
	 * Gets class field information for step 4 of the alogrithm. Also determines
	 * if the class already has a SVUID.
	 */
	public FieldVisitor visitField(final int access, final String name, final String desc, final String signature, final Object value) {
		if (computeSVUID) {
			if ("serialVersionUID".equals(name)) {
				// since the class already has SVUID, we won't be computing it.
				computeSVUID = false;
				hasSVUID = true;
			}
			/*
			 * Remember field for SVUID computation For field modifiers, only
			 * the ACC_PUBLIC, ACC_PRIVATE, ACC_PROTECTED, ACC_STATIC,
			 * ACC_FINAL, ACC_VOLATILE, and ACC_TRANSIENT flags are used when
			 * computing serialVersionUID values.
			 */
			int mods = access
					& (Opcodes.ACC_PUBLIC | Opcodes.ACC_PRIVATE | Opcodes.ACC_PROTECTED | Opcodes.ACC_STATIC | Opcodes.ACC_FINAL
							| Opcodes.ACC_VOLATILE | Opcodes.ACC_TRANSIENT);

			if ((access & Opcodes.ACC_PRIVATE) == 0 || (access & (Opcodes.ACC_STATIC | Opcodes.ACC_TRANSIENT)) == 0) {
				svuidFields.add(new Item(name, mods, desc));
			}
		}

		return super.visitField(access, name, desc, signature, value);
	}

	/*
	 * Add the SVUID if class doesn't have one
	 */
	public void visitEnd() {
		// compute SVUID and add it to the class
		if (computeSVUID && !hasSVUID) {
			try {
				cv.visitField(Opcodes.ACC_FINAL + Opcodes.ACC_STATIC, "serialVersionUID", "J", null, new Long(computeSVUID()));
			} catch (Throwable e) {
				throw new RuntimeException("Error while computing SVUID for " + name, e);
			}
		}

		super.visitEnd();
	}

	// ------------------------------------------------------------------------
	// Utility methods
	// ------------------------------------------------------------------------

	/**
	 * Returns the value of SVUID if the class doesn't have one already. Please
	 * note that 0 is returned if the class already has SVUID, thus use
	 * <code>isHasSVUID</code> to determine if the class already had an SVUID.
	 * 
	 * @return Returns the serial version UID
	 */
	protected long computeSVUID() throws IOException {
		ByteArrayOutputStream bos;
		DataOutputStream dos = null;
		long svuid = 0;

		try {
			bos = new ByteArrayOutputStream();
			dos = new DataOutputStream(bos);

			/*
			 * 1. The class name written using UTF encoding.
			 */
			dos.writeUTF(name.replace('/', '.'));

			/*
			 * 2. The class modifiers written as a 32-bit integer.
			 */
			dos.writeInt(access & (Opcodes.ACC_PUBLIC | Opcodes.ACC_FINAL | Opcodes.ACC_INTERFACE | Opcodes.ACC_ABSTRACT));

			/*
			 * 3. The name of each interface sorted by name written using UTF
			 * encoding.
			 */
			Arrays.sort(interfaces);
			for (int i = 0; i < interfaces.length; i++) {
				dos.writeUTF(interfaces[i].replace('/', '.'));
			}

			/*
			 * 4. For each field of the class sorted by field name (except
			 * private static and private transient fields):
			 * 
			 * 1. The name of the field in UTF encoding. 2. The modifiers of the
			 * field written as a 32-bit integer. 3. The descriptor of the field
			 * in UTF encoding
			 * 
			 * Note that field signatutes are not dot separated. Method and
			 * constructor signatures are dot separated. Go figure...
			 */
			writeItems(svuidFields, dos, false);

			/*
			 * 5. If a class initializer exists, write out the following: 1. The
			 * name of the method, <clinit>, in UTF encoding. 2. The modifier of
			 * the method, java.lang.reflect.Modifier.STATIC, written as a
			 * 32-bit integer. 3. The descriptor of the method, ()V, in UTF
			 * encoding.
			 */
			if (hasStaticInitializer) {
				dos.writeUTF("<clinit>");
				dos.writeInt(Opcodes.ACC_STATIC);
				dos.writeUTF("()V");
			} // if..

			/*
			 * 6. For each non-private constructor sorted by method name and
			 * signature: 1. The name of the method, <init>, in UTF encoding. 2.
			 * The modifiers of the method written as a 32-bit integer. 3. The
			 * descriptor of the method in UTF encoding.
			 */
			writeItems(svuidConstructors, dos, true);

			/*
			 * 7. For each non-private method sorted by method name and
			 * signature: 1. The name of the method in UTF encoding. 2. The
			 * modifiers of the method written as a 32-bit integer. 3. The
			 * descriptor of the method in UTF encoding.
			 */
			writeItems(svuidMethods, dos, true);

			dos.flush();

			/*
			 * 8. The SHA-1 algorithm is executed on the stream of bytes
			 * produced by DataOutputStream and produces five 32-bit values
			 * sha[0..4].
			 */
			byte[] hashBytes = computeSHAdigest(bos.toByteArray());

			/*
			 * 9. The hash value is assembled from the first and second 32-bit
			 * values of the SHA-1 message digest. If the result of the message
			 * digest, the five 32-bit words H0 H1 H2 H3 H4, is in an array of
			 * five int values named sha, the hash value would be computed as
			 * follows:
			 * 
			 * long hash = ((sha[0] >>> 24) & 0xFF) | ((sha[0] >>> 16) & 0xFF)
			 * << 8 | ((sha[0] >>> 8) & 0xFF) << 16 | ((sha[0] >>> 0) & 0xFF) <<
			 * 24 | ((sha[1] >>> 24) & 0xFF) << 32 | ((sha[1] >>> 16) & 0xFF) <<
			 * 40 | ((sha[1] >>> 8) & 0xFF) << 48 | ((sha[1] >>> 0) & 0xFF) <<
			 * 56;
			 */
			for (int i = Math.min(hashBytes.length, 8) - 1; i >= 0; i--) {
				svuid = (svuid << 8) | (hashBytes[i] & 0xFF);
			}
		} finally {
			// close the stream (if open)
			if (dos != null) {
				dos.close();
			}
		}

		return svuid;
	}

	/**
	 * Returns the SHA-1 message digest of the given value.
	 * 
	 * @param value
	 *            the value whose SHA message digest must be computed.
	 * @return the SHA-1 message digest of the given value.
	 */
	protected byte[] computeSHAdigest(final byte[] value) {
		try {
			return MessageDigest.getInstance("SHA").digest(value);
		} catch (Exception e) {
			throw new UnsupportedOperationException(e.toString());
		}
	}

	/**
	 * Sorts the items in the collection and writes it to the data output stream
	 * 
	 * @param itemCollection
	 *            collection of items
	 * @param dos
	 *            a <code>DataOutputStream</code> value
	 * @param dotted
	 *            a <code>boolean</code> value
	 * @exception IOException
	 *                if an error occurs
	 */
	private static void writeItems(final Collection itemCollection, final DataOutput dos, final boolean dotted) throws IOException {
		int size = itemCollection.size();
		Item[] items = (Item[]) itemCollection.toArray(new Item[size]);
		Arrays.sort(items);
		for (int i = 0; i < size; i++) {
			dos.writeUTF(items[i].name);
			dos.writeInt(items[i].access);
			dos.writeUTF(dotted ? items[i].desc.replace('/', '.') : items[i].desc);
		}
	}

	// ------------------------------------------------------------------------
	// Inner classes
	// ------------------------------------------------------------------------

	static class Item implements Comparable {

		final String name;

		final int access;

		final String desc;

		Item(final String name, final int access, final String desc) {
			this.name = name;
			this.access = access;
			this.desc = desc;
		}

		public int compareTo(final Object o) {
			Item other = (Item) o;
			int retVal = name.compareTo(other.name);
			if (retVal == 0) {
				retVal = desc.compareTo(other.desc);
			}
			return retVal;
		}
	}
}
